This invention relates generally to scanning probe microscopy (hereinafter “SPM”), and in particular, to an SPM probe formed with an integrated tip and to a method of printing with an SPM probe.
A scanning probe microscope is an important instrument for science and technology. One of the first scanning probe microscopes ever developed was called a Scanning Tunneling Microscope (STM). Another device within the scanning probe microscope family is an Atomic Force Microscope (hereinafter “AFM”). Nowadays, scanning probe microscopes are used to measure surface properties with atomic resolution. For example, scanning probe microscopes can be used to observe the structure of double helix of DNA. The capability of scanning probe microscopes has spread to include imaging of magnetic, optical, thermal, electrostatic charges, and many more. Scanning probe microscopes are also used for biological sensors as the static bending and resonant frequency of a scanning probe microscope is sensitive to the biochemical substances absorbed on it. Scanning probe microscopes are also used to perform nanolithography, such as dip pen nanolithography, and nanomanipulation, that is, interacting with objects on a molecular and an atomic scale.
Scanning probe microscopes use a probe having a flexible cantilever beam with a sharp tip attached at the distal end to perform their measurements. The cantilever beam is very soft, often with a force constant on the order of 0.1 N/m or less. The tip is used to interact with the surface of interest. In an AFM for example, the repulsive force between the surface and the tip causes the cantilever beam to bend. The minute amount of bending in the cantilever beam is picked up by using sensitive instruments, such as by optical deflection. By raster scanning the tip over a sample surface area, a local topological map can be produced. If the tip of the probe is relatively sharp, the topological map may be made with atomic resolution. Typically, the radius of curvature of tips range below 500 nanometers.
Needless to say, the SPM probe's cantilever beam with integrated tip is a performance limiting device in the overall scanning probe microscope system. Many research groups as well as companies that commercialize the scanning probe microscope spend much time to develop the cantilever beam and the tip of the probe. Using current fabrication methods, the cantilever beam is typically made of silicon nitride or single crystal silicon while the tip is typically etched by bulk silicon etching using wet etching chemicals or plasma etching. There are a number of major drawbacks to existing fabrication methods. First, the tips are made sharp using a special, time-sensitive processes that is not very efficient. Additionally, it is difficult to produce large arrays of tips with uniform sharpness. Moreover, the cantilevers are made of inorganic thin films such as silicon nitride or single crystal silicon which require a high temperature process and multiple process steps, such as a bulk silicon etch, to produce. Furthermore, certain processes require removal of a substrate upon which the probes are fabricated upon in order to remove the probe, and more specifically, the cantilever, from the substrate. Thus, a need exists for an improved method for fabricating an SPM probe.
Additionally, there is a need for an improved method for fabricating an SPM probe, including an array of SPM probes, using an efficient process, low cost materials, and a uniform profile. Such probes can then be used in a variety of ways, such as, for SPM, chemical/bio sensing, and nanolithography such as DPN.
There is also a need for an improved method for microcontact printing. Microcontact printing (μCP) is a soft lithography method capable of creating micro-scale structures on a microscopic level. Microcontact printing uses a stamp to transfer chemical or biological materials, also known as “ink,” onto a solid substrate. Microcontact printing creates impressions with the patterned stamp by placing the stamp near, or in contact with, the solid substrate. Microcontact printing does not form images by dragging the stamp across the solid substrate. Repeated contact with the solid substrate can form dots, lines, curves, and other such shapes. The stamp can be made of a variety of materials, such as metals, polymers, and elastomeric materials. One of the more commonly used elastomeric materials is poly(dimethylsiloxane) (PDMS), which is an inert material that is compatible with many chemical and biological inks. Microcontact printing has been used to pattern self-assembled monolayers of alkanethiols, proteins, chemical precursors, and other biological materials on a variety of substrates. Microcontact printing has also been used to transfer chemical or biological materials (inks) onto a solid substrate. However, microcontact printing invariably requires a dedicated photolithography mask to produce inverse mold features, and is limited with respect to multi-ink and alignment registration capabilities. Additionally, the production of the mask can be relatively costly and time consuming, particularly when sub-micrometer features are desired. Moreover, for many applications, such as the generation of proteomic and gene chips, well aligned, sub-micrometer scale features made of many different inks are desirable. Thus, a need exists for a less costly and less time consuming method for microcontact printing.